SIMPLE REACTIONS Predicting the products of dissolution The names and chemical formulas of some chemical compounds are written in the first two columns of the table below. Each compound is soluble in water. Imagine that a few tenths of a mole of each compound is dissolved in a liter of water. Then, write down in the third column of the table the chemical formula of the major chemical species that will be present in this solution. For example, you know water itself will be present, so you can begin each list with the chemical formula for water (H2O). Note: “major” chemical species are those present in concentrations greater than 10 mol/L. Compound Formula Major species present when dissolved in water Water H2O H2O Isopropanol C3H8O C3H8O Magnesium sulfate MgSO4 Mg2+, SO4^2- Ammonium bromide NH4Br NH4+, Br-
The Correct Answer and Explanation is:
Here is the correct completion of the table, along with a detailed explanation:
Completed Table:
| Compound | Formula | Major species present when dissolved in water |
|---|---|---|
| Water | H₂O | H₂O |
| Isopropanol | C₃H₈O | H₂O, C₃H₈O |
| Magnesium sulfate | MgSO₄ | H₂O, Mg²⁺, SO₄²⁻ |
| Ammonium bromide | NH₄Br | H₂O, NH₄⁺, Br⁻ |
Explanation
When compounds dissolve in water, they can either dissociate into ions (ionic compounds) or stay intact as molecules (molecular compounds). The major species present are those found in appreciable concentration in the solution (greater than 10−610^{-6}10−6 mol/L).
Water (H₂O) is the universal solvent and is always present in significant concentration.
Isopropanol (C₃H₈O) is a molecular compound (an alcohol) that is not ionic and does not dissociate into ions when dissolved in water. Instead, it mixes homogeneously and exists as intact C₃H₈O molecules. Thus, the major species are:
→ H₂O, C₃H₈O
Magnesium sulfate (MgSO₄) is an ionic compound consisting of Mg²⁺ (magnesium ion) and SO₄²⁻ (sulfate ion). It dissolves in water by dissociating into these ions. These ions are highly soluble and present in high concentration. Therefore, the major species are:
→ H₂O, Mg²⁺, SO₄²⁻
Ammonium bromide (NH₄Br) is also an ionic compound, made of the NH₄⁺ (ammonium ion) and Br⁻ (bromide ion). It dissolves completely in water and dissociates into its respective ions, so the major species are:
→ H₂O, NH₄⁺, Br⁻
This classification depends on solubility and the nature of the compound (ionic or molecular). Ionic compounds dissociate into ions, while molecular ones typically remain intact unless they undergo a chemical reaction with water (which is not the case here for isopropanol).
